Lubricating oil composition for hydraulic oil and method for producing the same

ABSTRACT

A lubricating oil composition for hydraulic oils including 10 to 99% by mass of a lubricant base oil (A) with a kinematic viscosity at 100° C. of 1 to 14 mm2/s, a viscosity index of 100 or more, and a pour point of 0° C. or lower, and 90 to 1% by mass of a liquid random copolymer (B) of ethylene and α-olefin prepared using a specific catalyst, wherein the total amount of (A) and (B) is 100% by mass, and having a kinematic viscosity at 100° C. of 10 to 300 mm2/s.

TECHNICAL FIELD

The present invention relates to a lubricating oil composition for hydraulic oils and a method for producing the same.

BACKGROUND ART

In industrial equipment machinery, particularly injection molding machines, machine tools, press processing machines, and machine tools/molding machines which require a large amount of work energy for forging press processing, and the like, hydraulic systems capable of converting compressed energy of a hydraulic pump to kinetic energy (work energy) are often used. In construction machines such as shovel-loader, wheel loader, skid-steer loader, and tractor, hydraulic systems are also widely used.

Meanwhile, global warming has advanced, and a reduction in amount of emission of carbon dioxide which is one of greenhouse gases is urgently required. With this being the situation, there is demand for a reduction in power consumption in hydraulic systems used in various kinds of industrial fields as described above. For a reduction in power consumption of the hydraulic systems, an approach for reducing the viscosity of lubricating oil to reduce fluid resistance in hydraulic pumps and pipes is effective. When the viscosity of the lubricating oil in a range from a low temperature to a normal temperature is reduced, an energy loss during start-up can be largely reduced. However, when the viscosity of lubricating oil is reduced, internal leakage during operation at high temperatures may occur, or an oil film may be lost. Thus, lubricity may be deteriorated to cause a frictional loss. A lubricating oil which has excellent temperature viscosity properties, that is, in which a fluid loss is unlikely to be caused under low temperatures, and a reduction in viscosity at high temperatures is small is required (Non Patent Literature 1).

In order to meet such demands, a hydraulic oil using ethylene-α-olefin having excellent temperature viscosity properties as a base oil and a viscosity modifying agent is investigated (Patent Literatures 1 and 2). However, disclosed compositions have high viscosity, and are insufficient for the purpose of energy saving. Single use of a synthetic oil (poly-α-olefin) having sufficiently low viscosity and excellent temperature viscosity properties has been investigated, but there is still room for investigation (Patent Literature 3).

Patent Literature 4 discloses a lubricating oil composition which has remarkably excellent temperature viscosity properties, namely, oil film retention properties at high temperatures and low-temperature viscosity properties, is suitably applicable to a hydraulic oil, and contains a specific lubricant base oil and a specific ethylene-α-olefin copolymer.

Moreover, Patent Literature 5 describes a method for producing a liquid random copolymer of ethylene and α-olefin, wherein further described is that this copolymer is useful as a lubricating oil.

CITATION LIST Patent Literature

-   Patent Literature 1: JP S63-022897 A -   Patent Literature 2: JP H05-070788 A -   Patent Literature 3: JP 2002-519448 A -   Patent Literature 4: JP 2016-069408 A -   Patent Literature 5: EP 2921509 A1

Non Patent Literature

-   Non Patent Literature 1: Illustrated guide to the introductory     basics of industrial lubricating oil (2011); Author/Editor:     Lubricants Department, Lubricant Technology 2^(nd) section of     Idemitsu Kosan Co Ltd, published by Nikkan Kogyo Shimbun, Ltd [The     Daily Industrial News]

SUMMARY OF INVENTION Technical Problem

However, there was further room for improvement in conventional lubricating oil compositions, from the perspective of providing a lubricating oil composition for hydraulic oils having remarkably excellent temperature viscosity properties, namely, oil film retention properties at high temperatures and low-temperature viscosity properties, and further having excellent thermal and oxidation stability.

Solution to Problem

The present inventors have keenly investigated the development of a lubricating oil composition for hydraulic oils having excellent performance, and as a result, discovered that the aforementioned problem can be solved with a lubricating oil composition which contains, with a specific lubricant base oil, an ethylene-α-olefin (co)polymer prepared by means of a specific catalyst, and satisfies specific conditions, thus arriving at the perfection of the present invention. The present invention specifically mentions the below aspect.

[1]

A lubricating oil composition for hydraulic oils, comprising 10 to 99% by mass of a lubricant base oil (A) having the properties of the below (A1) to (A3), 90 to 1% by mass of a liquid random copolymer (B) of ethylene and α-olefin, the liquid random copolymer (B) being prepared by the below method (α), wherein the total amount of the lubricant base oil (A) and the copolymer (B) is 100% by mass, the lubricating oil composition having the properties of the below (C1).

(A1) The lubricant base oil has a kinematic viscosity at 100° C. of 1 to 14 mm²/s. (A2) The lubricant base oil has a viscosity index of 100 or more. (A3) The lubricant base oil has a pour point of 0° C. or lower. (C1) The lubricating oil composition for hydraulic oils has a kinematic viscosity at 40° C. of 10 to 300 mm²/s.

(Method (α))

A method (α) for preparing a liquid random copolymer of ethylene and α-olefin, comprising a step of carrying out solution polymerization of ethylene and α-olefin having 3 to 20 carbon atoms, under a catalyst system comprising

(a) a bridged metallocene compound represented by the following Formula 1, and (b) at least one compound selected from a group consisting of

(i) an organoaluminum oxy-compound, and

(ii) a compound which reacts with the bridged metallocene compound to form an ion pair.

[In Formula 1, R¹, R², R³, R⁴, R⁵, R⁸, R⁹ and R¹² are respectively and independently hydrogen atom, hydrocarbon group or silicon-containing hydrocarbon group, and adjoining groups are optionally connected to each other to form a ring structure,

R⁶ and R¹¹, being the same, are hydrogen atom, hydrocarbon group or silicon-containing hydrocarbon group,

R⁷ and R¹⁰, being the same, are hydrogen atom, hydrocarbon group or silicon-containing hydrocarbon group,

R⁶ and R⁷ are optionally connected to hydrocarbon having 2 to 3 carbon atoms to form a ring structure,

R¹¹ and R¹⁰ are optionally connected to hydrocarbon having 2 to 3 carbon atoms to form a ring structure,

R⁶, R⁷, R¹⁰ and R¹¹ are not hydrogen atom at the same time;

Y is a carbon atom or silicon atom;

R¹³ and R¹⁴ are independently aryl group;

M is Ti, Zr or Hf;

Q is independently halogen, hydrocarbon group, an anionic ligand or a neutral ligand which can be coordinated to a lone pair of electrons; and

j is an integer of 1 to 4.]

[2]

The lubricating oil composition for hydraulic oils of the aforementioned [1], wherein in the metallocene compound represented by the above Formula 1, at least one among substituents (R¹, R², R³ and R⁴) bonded to a cyclopentadienyl group is a hydrocarbon group having 4 or more carbon atoms.

[3]

The lubricating oil composition for hydraulic oils of the aforementioned [1] or [2], wherein R⁶ and R¹¹, being the same, are hydrocarbon groups having 1 to 20 carbon atoms.

[4]

The lubricating oil composition for hydraulic oils of any of the aforementioned [1] to [3], wherein in the metallocene compound represented by the above Formula 1, substituent (R² or R³) bonded to the 3-position of the cyclopentadienyl group is a hydrocarbon group.

[5]

The lubricating oil composition for hydraulic oils of the aforementioned [4], wherein in the metallocene compound represented by the above Formula 1, the hydrocarbon group (R² or R³) bonded to the 3-position of the cyclopentadienyl group is an n-butyl group.

[6]

The lubricating oil composition for hydraulic oils of any of the aforementioned [1] to [5], wherein in the metallocene compound represented by the above Formula 1, substituents (R⁶ and R¹¹) bonded to the 2-position and 7-position of the fluorenyl group are all tert-butyl groups.

[7]

The lubricating oil composition for hydraulic oils of any of the aforementioned [1] to [6], wherein the compound which reacts with the bridged metallocene compound to form an ion pair is a compound represented by the following Formula 6.

[In Formula 6, R^(e+) is H⁺, a carbenium cation, an oxonium cation, an ammonium cation, a phosphonium cation, a cycloheptyltrienyl cation, or a ferrocenium cation having a transition metal, and R^(f) to R^(i) each is independently a hydrocarbon group having 1 to 20 carbon atoms.]

[8]

The lubricating oil composition for hydraulic oils of the aforementioned [7], wherein the ammonium cation is a dimethylanilinium cation.

[9]

The lubricating oil composition for hydraulic oils of the aforementioned [7] or [8], wherein the catalyst system further comprises an organoaluminum compound selected from a group consisting of trimethyl aluminum and triisobutyl aluminum.

[10]

The lubricating oil composition for hydraulic oils of any of the aforementioned [1] to [9], wherein a content of the liquid random copolymer (B) is 1 to 20% by mass.

[11]

A lubricating oil composition for hydraulic oils, comprising 10 to 99% by mass of a lubricant base oil (A) having the properties of the below (A1) to (A3), 90 to 1% by mass of a liquid random copolymer of ethylene and α-olefin having the properties of the below (B1) to (B5), wherein the total amount of the lubricant base oil (A) and the copolymer is 100% by mass, the lubricating oil composition having the properties of the below (C1).

(A1) The lubricant base oil has a kinematic viscosity at 100° C. of 1 to 14 mm²/s. (A2) The lubricant base oil has a viscosity index of 100 or more. (A3) The lubricant base oil has a pour point of 0° C. or lower. (B1) The liquid random copolymer comprises 40 to 60 mol % of ethylene units and 60 to 40 mol % of α-olefin units having 3 to 20 carbon atoms. (B2) The liquid random copolymer has a number average molecular weight (Mn) of 500 to 10,000 and a molecular weight distribution (Mw/Mn, Mw is the weight average molecular weight) of 3 or less, as measured by gel permeation chromatography (GPC). (B3) The liquid random copolymer has a kinematic viscosity at 100° C. of 30 to 5,000 mm²/s. (B4) The liquid random copolymer has a pour point of 30 to −45° C. (B5) The liquid random copolymer has a Bromine Number of 0.1 g/100 g or less. (C1) The lubricating oil composition for hydraulic oils has a kinematic viscosity at 40° C. of 10 to 300 mm²/s. [12]

The lubricating oil composition for hydraulic oils of any of the aforementioned [1] to [11], wherein the lubricant base oil (A) further satisfies the below (A4) to (A6).

(A4) The lubricant base oil has a kinematic viscosity at 100° C. of 1 to 10 mm²/s. (A5) The lubricant base oil has a viscosity index of 110 or more. (A6) The lubricant base oil has a pour point of −10° C. or lower. [13]

The lubricating oil composition for hydraulic oils of any of the aforementioned [1] to [12], wherein 30 to 100% by mass of the lubricant base oil (A) is a mineral oil.

[14]

The lubricating oil composition for hydraulic oils of any of the aforementioned [1] to [12], wherein 30 to 100% by mass of the lubricant base oil (A) is a synthetic oil, and the synthetic oil is poly-α-olefin (PAO) and/or an ester oil.

[15]

The lubricating oil composition for hydraulic oils of any of the aforementioned [1] to [14], wherein the kinematic viscosity at 40° C. is 20 to 100 mm²/s.

[16]

A hydraulic oil for machine tools or molders comprising a lubricating oil composition for hydraulic oils of any of the aforementioned [1] to [15].

[17]

A method for producing a lubricating oil composition for hydraulic oils, comprising the steps of:

preparing a liquid random copolymer (B) of ethylene and α-olefin by the following method (α); and

preparing a lubricating oil composition for hydraulic oils by mixing a lubricant base oil (A) having the properties of the below (A1) to (A3) in an amount of 10 to 99% by mass in the lubricating oil composition with the liquid random copolymer (B) in an amount of 1 to 90% by mass in the lubricating oil composition, wherein the total amount of the lubricant base oil (A) and the copolymer (B) is 100% by mass, the composition having the properties of the below (C1).

(A1) The lubricant base oil has a kinematic viscosity at 100° C. of 1 to 14 mm²/s. (A2) The lubricant base oil has a viscosity index of 100 or more. (A3) The lubricant base oil has a pour point of 0° C. or lower. (C1) The lubricating oil composition for hydraulic oils has a kinematic viscosity at 40° C. of 10 to 300 mm²/s.

(Method (α))

A method (α) for preparing a liquid random copolymer of ethylene and α-olefin, comprising a step of carrying out solution polymerization of ethylene and α-olefin having 3 to 20 carbon atoms, under a catalyst system comprising

(a) a bridged metallocene compound represented by the following Formula 1, and (b) at least one compound selected from a group consisting of

(i) an organoaluminum oxy-compound, and

(ii) a compound which reacts with the bridged metallocene compound to form an ion pair.

[In Formula 1, R¹, R², R³, R⁴, R⁵, R⁸, R⁹ and R¹² are

respectively and independently hydrogen atom, hydrocarbon group or silicon-containing hydrocarbon group, and adjoining groups are optionally connected to each other to form a ring structure,

R⁶ and R¹¹, being the same, are hydrogen atom, hydrocarbon group or silicon-containing hydrocarbon group,

R⁷ and R¹⁰, being the same, are hydrogen atom, hydrocarbon group or silicon-containing hydrocarbon group,

R⁶ and R⁷ are optionally connected to hydrocarbon having 2 to 3 carbon atoms to form a ring structure,

R¹¹ and R¹⁰ are optionally connected to hydrocarbon having 2 to 3 carbon atoms to form a ring structure,

R⁶, R⁷, R¹⁰ and R¹¹ are not hydrogen atom at the same time;

Y is a carbon atom or silicon atom;

R¹³ and R¹⁴ are independently aryl group;

M is Ti, Zr or Hf;

Q is independently halogen, hydrocarbon group, an anionic ligand or a neutral ligand which can be coordinated to a lone pair of electrons; and

j is an integer of 1 to 4.]

Advantageous Effects of Invention

The lubricating oil composition for hydraulic oils of the present invention has remarkably excellent temperature viscosity properties, namely, oil film retention properties at high temperatures and low-temperature viscosity properties, and further excellent thermal and oxidation stability. The lubricating oil composition is suitably applicable to hydraulic oils, particularly hydraulic oils for machine tools/molding machines.

DESCRIPTION OF EMBODIMENTS

The lubricating oil composition for hydraulic oils according to the present invention (hereinafter, also referred to merely as “lubricating oil composition”) will be described in detail below.

The lubricating oil composition for hydraulic oils according to the present invention contains a lubricant base oil (A), and a liquid random copolymer (B) of ethylene and α-olefin prepared by a method (α) (herein also referred to as “ethylene-α-olefin copolymer (B)”), wherein a kinematic viscosity at 40° C. and a viscosity index within specific ranges.

<(A) Lubricant Base Oil>

The lubricant base oil (A) has the properties of the below (A1) to (A3).

(A1) The lubricant base oil has a kinematic viscosity at 100° C. of 1 to 14 mm²/s

The value of this kinematic viscosity at 100° C. is that as measured in accordance with the method described in JIS K2283. The kinematic viscosity at 100° C. of the lubricant base oil (A) is 1 to 14 m²/s, preferably 1 to 10 mm²/s, and more preferably 2 to 8 mm²/s. With a kinematic viscosity at 100° C. in this range, the lubricating oil composition of the present invention is excellent in terms of balance between volatility and temperature viscosity properties.

(A2) The lubricant base oil has a viscosity index of 100 or more

The value of this viscosity index is that as measured in accordance with the method described in JIS K2283. The viscosity index of the lubricant base oil (A) is 100 or more, preferably 110 or more, and further preferably 120 or more. With a viscosity index in this range, the lubricating oil composition of the present invention has excellent temperature viscosity properties.

(A3) The lubricant base oil has a pour point of 0° C. or lower

The value of this pour point is that as measured in accordance with the method described in ASTM D97. The pour point of the lubricant base oil (A) is 0° C. or lower, preferably −10° C. or lower, more preferably −20° C. or lower, and further preferably −30° C. or lower. With a pour point in this range, the lubricating oil composition of the present invention has excellent low-temperature viscosity properties.

In the lubricant base oil used in the present invention, performance and quality such as viscosity properties, heat resistance and oxidation stability, will differ depending on the producing and refining processes etc. of the lubricant base oil. In general, the lubricant base oil is classified broadly into a mineral oil and a synthetic oil. The API (American Petroleum Institute) categorizes lubricant base oil into five types: Group I, II, III, IV and V. These API categories are defined in the API Publication 1509, 15^(th) Edition, Appendix E, April 2002, and are as shown in Table 1. The lubricant base oil (A) may be a mineral oil or a synthetic oil, and may be any of Group I to V in the API categories. Details are described as follows.

TABLE 1 Saturated Viscosity hydrocarbon Sulfur portion ^(*3) Group Type index ^(*1) portion ^(*2) (vol %) (% by weight) I Mineral 80 to 120 <90 >0.03 oil II Mineral 80 to 120 ≥90 ≤0.03 oil III Mineral ≥120 ≥90 ≤0.03 oil IV Poly-α-olefin V Lubricant base material other than the aforementioned ^(*1)Measured in accordance with ASTM D445 (JIS K2283) ^(*2)Measured in accordance with ASTM D3238 ^(*3)Measured in accordance with ASTM D4294 (JIS K2541) ^(*4)Mineral oils whose saturated hydrocarbon portion is less than 90 vol % and sulfur portion is less than 0.03% by weight, or whose saturated hydrocarbon portion is 90 vol % or more and sulfur portion exceeds 0.03% by weight, are included in Group I.

<Mineral Oil>

The mineral oil is ascribed to Groups I to III of the aforementioned API categories.

The quality of the mineral oil is as mentioned above, where the aforementioned respective qualities of mineral oil are obtainable depending on the refining method. Exemplifications of the mineral oil specifically include: a lubricant base oil, in which a lubricating oil fraction obtained by reduced pressure distillation of an atmospheric residue which is obtainable by the atmospheric distillation of crude oil, is refined by one or more treatments such as solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, hydrorefining; or a lubricant base oil of wax isomerized mineral oil.

Moreover, a Gas-to-Liquid (GTL) base oil obtained by the Fisher-Tropsch method is a base oil which can also be suitably utilized as Group III mineral oil. Such GTL base oil is also handled as Group III+ lubricant base oil, which are described e.g. in the following Patent Literatures: EP0776959, EP0668342, WO97/21788, WO00/15736, WO00/14188, WO00/14187, WO00/14183, WO00/14179, WO00/08115, WO99/41332, EP1029029, WO01/18156 and WO01/57166.

<Synthetic Oil>

The synthetic oil is ascribed to Group IV or Group V of the aforementioned API categories.

Poly-α-olefins, which are ascribed to Group IV, can be obtained by oligomerization with an acid catalyst such as boron trifluoride and a chromic acid catalyst, as described in e.g. U.S. Pat. Nos. 3,382,291, 3,763,244, 5,171,908, 3,780,128, 4,032,591, JP H01-163136 A, U.S. Pat. Nos. 4,967,032 and 4,926,004. Poly-α-olefins can also be obtained processes using a catalyst system containing a complex of a transition metal such as zirconium, titanium, or hafnium, which includes a metallocene compound as described in patent literatures, JP S63-37102 A, JP 2005-200447 A, JP 2005-200448 A, JP 2009-503147 A, and JP 2009-501836 A. If utilizing a poly-α-olefin as the lubricant base oil (A), a lubricating oil composition having remarkably excellent temperature viscosity properties, low-temperature viscosity properties, as well as heat resistance is obtainable.

Poly-α-olefins are also industrially available, where those with a kinematic viscosity at 100° C. of 2 mm²/s to 150 mm²/s are commercially available. In particular, use of a poly-α-olefin with a kinematic viscosity at 100° C. of 2 to 14 mm²/s is preferred since a lubricating oil composition having excellent temperature viscosity properties is obtained. Examples include the NEXBASE 2000 series (made by NESTE), Spectrasyn (made by ExxonMobil Chemical), Durasyn (made by INEOS Oligomers), and Synfluid (made by Chevron Phillips Chemical).

As the synthetic oil ascribed to Group V, examples include alkyl benzenes, alkyl naphthalenes, isobutene oligomers and hydrides thereof, paraffins, polyoxy alkylene glycol, dialkyl diphenylether, polyphenylether, and esters.

Most of the alkyl benzenes and alkyl naphthalenes are usually dialkyl benzene or dialkyl naphthalene whose alkyl chain length has 6 to 14 carbon atoms, where such alkyl benzenes or alkyl naphthalenes are produced by the Friedel-Crafts alkylation reaction of benzene or naphthalene with olefin. In the production of alkyl benzenes or alkyl naphthalenes, the alkylated olefin to be utilized may be a linear or branched olefin, or may be a combination of these. These production processes are described in e.g. U.S. Pat. No. 3,909,432.

Moreover, as the ester, fatty acid esters are preferred from the perspective of compatibility with the ethylene-α-olefin copolymer (B).

Although there are no particular limitations on the fatty acid esters, examples include fatty acid esters consisting of only carbon, oxygen or hydrogen as mentioned below, where the examples include monoesters prepared from a monobasic acid and alcohol; diesters prepared from dibasic acid and alcohol, or from a diol with a monobasic acid or an acid mixture; or polyolesters prepared by reacting a monobasic acid or an acid mixture with a diol, triol (e.g. trimethylolpropane), tetraol (e.g. pentaerythritol), hexol (e.g. dipentaerythritol) etc. Examples of these esters include ditridecyl glutarate, di-2-ethyl hexyl adipate, diisodecyl adipate, ditridecyl adipate, di-2-ethyl hexyl sebacate, tridecyl pelargonate, di-2-ethyl hexyl adipate, di-2-ethyl hexyl azelate, trimethylolpropane caprylate, trimethylolpropane pelargonate, trimethylolpropane triheptanoate, pentaerythritol-2-ethyl hexanoate, pentaerythritol pelargonate, and pentaerythritol tetraheptanoate.

From the perspective of the compatibility with the ethylene-α-olefin copolymer (B), an alcohol having two or more functional hydroxyl groups is preferred as the alcohol moiety constituting the ester, and a fatty acid having 8 or more carbon atoms is preferred as the fatty acid moiety. However, a fatty acid having 20 or fewer carbon atoms, which is easily industrially available, is superior in terms of the manufacturing cost of the fatty acid. The effect of the present invention is also sufficiently exhibited with the use of one fatty acid constituting an ester, or with the use of a fatty acid ester prepared by means of two or more acid mixtures. Examples of fatty acid esters more specifically include a mixed triester of trimethylolpropane with lauric acid and stearic acid, and diisodecyl adipate, where these are preferable in terms of compatibility of saturated hydrocarbon components such as the ethylene-α-olefin copolymer (B), with stabilizers such as antioxidants, corrosion preventing agents, anti-wear agents, friction modifying agents, pour point lowering agents, anti-rust agents and anti-foamers mentioned below and having a polar group.

When utilizing a synthetic oil, particularly a poly-α-olefin as the lubricant base oil (A), it is preferable that the lubricating oil composition of the present invention contain a fatty acid ester in an amount of 5 to 20% by mass with respect to 100% by mass of the entire weight of the lubricating oil composition. By containing a fatty acid ester of 5% by mass or more, good compatibility is obtainable with the lubricating oil sealing material such as resins and elastomers inside the internal combustion engines and industrial machinery of all types. Specifically, swelling of the lubricating oil sealing material can be suppressed. From the perspective of oxidation stability or heat resistance, the amount of ester is preferably 20% by mass or less. When mineral oil is contained in the lubricating oil composition, a fatty acid ester is not necessarily required, because the mineral oil per se has a swelling suppression effect of the lubricating oil sealing agent.

The synthetic oil is preferred in terms of excellent heat resistance and temperature viscosity properties as compared to the mineral oil.

In the lubricating oil composition of the present invention, the synthetic oil or mineral oil may be used alone as the lubricant base oil (A), or any mixture etc. of two or more lubricating oils selected from the synthetic oil and mineral oil may be used as the lubricant base oil (A).

<(B) Ethylene-α-Olefin Copolymer>

The ethylene-α-olefin copolymer (B) is a liquid random copolymer (B) of ethylene and α-olefin prepared by the following method (α).

(Method (α))

A method (α) for preparing a liquid random copolymer of ethylene and α-olefin, comprising a step of carrying out solution polymerization of ethylene and α-olefin having 3 to 20 carbon atoms, under a catalyst system containing

(a) a bridged metallocene compound represented by the following Formula 1, and (b) at least one compound selected from a group consisting of

(i) an organoaluminum oxy-compound, and

(ii) a compound which reacts with the bridged metallocene compound to form an ion pair.

[In Formula 1, R¹, R², R³, R⁴, R⁵, R⁸, R⁹ and R¹² are respectively and independently hydrogen atom, hydrocarbon group or silicon-containing hydrocarbon group, and adjoining groups are optionally connected to each other to form a ring structure,

R⁶ and R¹¹, being the same, are hydrogen atom, hydrocarbon group or silicon-containing hydrocarbon group,

R⁷ and R¹⁰, being the same, are hydrogen atom, hydrocarbon group or silicon-containing hydrocarbon group,

R⁶ and R⁷ are optionally connected to hydrocarbon having 2 to 3 carbon atoms to form a ring structure,

R¹¹ and R¹⁰ are optionally connected to hydrocarbon having 2 to 3 carbon atoms to form a ring structure,

R⁶, R⁷, R¹⁰ and R¹¹ are not hydrogen atom at the same time;

Y is a carbon atom or silicon atom;

R¹³ and R¹⁴ are independently aryl group;

M is Ti, Zr or Hf;

Q is independently halogen, hydrocarbon group, an anionic ligand or a neutral ligand which can be coordinated to a lone pair of electrons; and

j is an integer of 1 to 4.]

Here, the hydrocarbon group has 1 to 20 carbon atoms, preferably 1 to 15 atoms, and more preferably 4 to 10 carbon atoms, and means for example an alkyl group, aryl group etc. The aryl group has 6 to 20 carbon atoms, and preferably 6 to 15 carbon atoms.

Examples of the silicon-containing hydrocarbon group include an alkyl or aryl group having 3 to 20 carbon atoms which contains 1 to 4 silicon atoms, and in more detail includes trimethylsilyl group, tert-butyldimethylsilyl group, triphenylsilyl group etc.

In the bridged metallocene compound represented by Formula 1, cyclopentadienyl group may be substituted or unsubstituted.

In the bridged metallocene compound represented by Formula 1,

(i) it is preferable that at least one among substituents (R¹, R², R³ and R⁴) bonded to cyclopentadienyl group is a hydrocarbon group,

(ii) it is more preferable that at least one among substituents (R¹, R², R³ and R⁴) is a hydrocarbon group having 4 or more carbon atoms,

(iii) it is most preferable that substituent (R² or R³) bonded to the 3-position of the cyclopentadienyl group is a hydrocarbon group having 4 or more carbon atoms (for example an n-butyl group).

In case where at least two among R¹, R², R³ and R⁴ are substituents (that is, being not hydrogen atom), the above-mentioned substituents may be the same or be different, and it is preferable that at least one substituent is a hydrocarbon group having 4 or more carbon atoms.

In the metallocene compound represented by Formula 1, R⁶ and R¹¹ bonded to fluorenyl group are the same, R⁷ and R¹⁰ are the same, but R⁶, R⁷, R¹⁰ and R¹¹ are not hydrogen atom at the same time. In high-temperature solution polymerization of poly-α-olefin, in order to improve the polymerization activity, preferably neither R⁶ nor R¹¹ is hydrogen atom, and more preferably none of R⁶, R⁷, R¹⁰ and R¹¹ is hydrogen atom. For example, R⁶ and R¹¹ bonded to the 2-position and 7-position of the fluorenyl group are the same hydrocarbon group having 1 to 20 carbon atoms, and preferably all tert-butyl groups, and R⁷ and R¹⁰ are the same hydrocarbon group having 1 to 20 carbon atoms, and preferably all tert-butyl groups.

The main chain part (bonding part, Y) connecting the cyclopentadienyl group and the fluorenyl group is a cross-linking section of two covalent bonds comprising one carbon atom or silicon atom, as a structural bridge section imparting steric rigidity to the bridged metallocene compound represented by Formula 1. Cross-linking atom (Y) in the cross-linking section has two aryl groups (R¹³ and R¹⁴) which may be the same or different. Therefore, the cyclopentadienyl group and the fluorenyl group are bonded by the covalent bond cross-linking section containing an aryl group. Examples of the aryl group include a phenyl group, naphthyl group, anthracenyl group, and a substituted aryl group (which is formed by substituting one or more aromatic hydrogen (sp²-type hydrogen) of a phenyl group, naphthyl group or anthracenyl group, with substituents). Examples of substituents in the aryl group include a hydrocarbon group having 1 to 20 carbon atoms, a silicon-containing hydrocarbon group having 1 to 20 carbon atoms, a halogen atom etc., and preferably include a phenyl group. In the bridged metallocene compound represented by Formula 1, preferably R¹³ and R¹⁴ are the same in view of easy production.

In the bridged metallocene compound represented by Formula 1, Q is preferably a halogen atom or hydrocarbon group having 1 to 10 carbon atoms. The halogen atom includes fluorine, chlorine, bromine or iodine. The hydrocarbon group having 1 to 10 carbon atoms includes methyl, ethyl, n-propyl, isopropyl, 2-methylpropyl, 1,1-dimethylpropyl, 2,2-dimethylpropyl, 1,1-diethylpropyl, 1-ethyl-1-methylpropyl, 1,1,2,2-tetramethylpropyl, sec-butyl, tert-butyl, 1,1-dimethylbutyl, 1,1,3-trimethylbutyl, neopentyl, cyclohexyl methyl, cyclohexyl, 1-methyl-1-cyclohexyl etc. Further, when j is an integer of 2 or more, Q may be the same or different.

Examples of such bridged metallocene compounds (a) include:

ethylene [η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)](η⁵-fluorenyl) zirconium dichloride, ethylene [η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)][η⁵-(3,6-di-tert-butyl fluorenyl)] zirconium dichloride, ethylene [η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)][η⁵-(2,7-di-tert-butyl fluorenyl)] zirconium dichloride, ethylene [η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)] (octamethyl octahydrodibenzofluorenyl) zirconium dichloride, ethylene [η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)](benzofluorenyl) zirconium dichloride, ethylene [η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)] (dibenzofluorenyl) zirconium dichloride, ethylene [η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)] (octahydrodibenzofluorenyl) zirconium dichloride, ethylene [η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)][η⁵-(2,7-diphenyl-3,6-di-tert-butyl fluorenyl)] zirconium dichloride, ethylene [η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)] [η⁵-(2,7-dimethyl-3,6-di-tert-butyl fluorenyl)] zirconium dichloride;

ethylene [η⁵-(3-tert-butyl cyclopentadienyl)] (η⁵-fluorenyl) zirconium dichloride, ethylene [η⁵-(3-tert-butyl cyclopentadienyl)] [η⁵-(3,6-di-tert-butyl fluorenyl)]zirconium dichloride, ethylene [η⁵-(3-tert-butyl cyclopentadienyl)][η5-(2,7-di-tert-butyl fluorenyl)]zirconium dichloride, ethylene [η⁵-(3-tert-butyl cyclopentadienyl)] (octamethyl octahydrodibenzofluorenyl) zirconium dichloride, ethylene [η⁵-(3-tert-butyl cyclopentadienyl)] (benzofluorenyl) zirconium dichloride, ethylene [η⁵-(3-tert-butyl cyclopentadienyl)](dibenzofluorenyl) zirconium dichloride, ethylene [η⁵-(3-tert-butyl cyclopentadienyl)] (octahydrodibenzofluorenyl) zirconium dichloride, ethylene [η⁵-(3-tert-butyl cyclopentadienyl)][η⁵-(2,7-diphenyl-3,6-di-tert-butyl fluorenyl)] zirconium dichloride, ethylene [η⁵-(3-tert-butyl cyclopentadienyl)][η⁵-(2,7-dimethyl-3,6-di-tert-butyl fluorenyl)] zirconium dichloride;

ethylene [η⁵-(3-n-butyl cyclopentadienyl)] (η⁵-fluorenyl) zirconium dichloride, ethylene [η⁵-(3-n-butyl cyclopentadienyl)] [η⁵-(3,6-di-tert-butyl fluorenyl)]zirconium dichloride, ethylene [η⁵-(3-n-butyl cyclopentadienyl)][η⁵-(2,7-di-tert-butyl fluorenyl)]zirconium dichloride, ethylene [η⁵-(3-n-butyl cyclopentadienyl)] (octamethyl octahydrodibenzofluorenyl) zirconium dichloride, ethylene [η⁵-(3-n-butyl cyclopentadienyl)] (benzofluorenyl) zirconium dichloride, ethylene [η⁵-(3-n-butyl cyclopentadienyl)] (dibenzofluorenyl) zirconium dichloride, ethylene [η⁵-(3-n-butyl cyclopentadienyl)] (octahydrodibenzofluorenyl) zirconium dichloride, ethylene [η⁵-(3-n-butyl cyclopentadienyl)] [η⁵-(2,7-diphenyl-3,6-di-tert-butyl fluorenyl)] zirconium dichloride, ethylene [η⁵-(3-n-butyl cyclopentadienyl)] [η⁵-(2,7-dimethyl-3,6-di-tert-butyl fluorenyl)] zirconium dichloride;

diphenylmethylene [η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)](η⁵-fluorenyl) zirconium dichloride, diphenylmethylene [η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)] [η⁵-(3,6-di-tert-butyl fluorenyl)]zirconium dichloride, diphenylmethylene [η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)] [η⁵-(2,7-di-tert-butyl fluorenyl)]zirconium dichloride, diphenylmethylene [η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)] (octamethyl octahydrodibenzofluorenyl) zirconium dichloride, diphenylmethylene [η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)] (benzofluorenyl) zirconium dichloride, diphenylmethylene [η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)] (dibenzofluorenyl) zirconium dichloride, diphenylmethylene [η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)] (octahydrodibenzofluorenyl) zirconium dichloride, diphenylmethylene [η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)][η⁵-(2,7-diphenyl-3,6-di-tert-butyl fluorenyl)] zirconium dichloride, diphenylmethylene [η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)] [η⁵-(2,7-dimethyl-3,6-di-tert-butyl fluorenyl)] zirconium dichloride;

diphenylmethylene [η⁵-(3-tert-butyl cyclopentadienyl)](η⁵-fluorenyl) zirconium dichloride, diphenylmethylene [η⁵-(3-tert-butyl cyclopentadienyl)][η⁵-(3,6-di-tert-butyl fluorenyl)] zirconium dichloride, diphenylmethylene [η⁵-(3-tert-butyl cyclopentadienyl)] [η⁵-(2,7-di-tert-butyl fluorenyl)] zirconium dichloride, diphenylmethylene [η⁵-(3-tert-butyl cyclopentadienyl)] (octamethyl octahydrodibenzofluorenyl) zirconium dichloride, diphenylmethylene [η⁵-(3-tert-butyl cyclopentadienyl)](benzofluorenyl) zirconium dichloride, diphenylmethylene [η⁵-(3-tert-butyl cyclopentadienyl)] (dibenzofluorenyl) zirconium dichloride, diphenylmethylene [η⁵-(3-tert-butyl cyclopentadienyl)] (octahydrodibenzofluorenyl) zirconium dichloride, diphenylmethylene [η⁵-(3-tert-butyl cyclopentadienyl)][η⁵-(2,7-diphenyl-3,6-di-tert-butyl fluorenyl)] zirconium dichloride, diphenylmethylene [η⁵-(3-tert-butyl cyclopentadienyl)] [η⁵-(2,7-dimethyl-3,6-di-tert-butyl fluorenyl)] zirconium dichloride; diphenylmethylene [η⁵-(3-n-butyl cyclopentadienyl)](η⁵-fluorenyl) zirconium dichloride, diphenylmethylene [η⁵-(3-n-butyl cyclopentadienyl)] [η⁵-(3,6-di-tert-butyl fluorenyl)]zirconium dichloride, diphenylmethylene [η⁵-(3-n-butyl cyclopentadienyl)][η⁵-(2,7-di-tert-butyl fluorenyl)]zirconium dichloride, diphenylmethylene [η⁵-(3-n-butyl cyclopentadienyl)] (octamethyl octahydrodibenzofluorenyl) zirconium dichloride, diphenylmethylene [η⁵-(3-n-butyl cyclopentadienyl)] (benzofluorenyl) zirconium dichloride, diphenylmethylene [η⁵-(3-n-butyl cyclopentadienyl)](dibenzofluorenyl) zirconium dichloride, diphenylmethylene [η⁵-(3-n-butyl cyclopentadienyl)] (octahydrodibenzofluorenyl) zirconium dichloride, diphenylmethylene [η⁵-(3-n-butyl cyclopentadienyl)][η⁵-(2,7-diphenyl-3,6-di-tert-butyl fluorenyl)] zirconium dichloride, diphenylmethylene [η⁵-(3-n-butyl cyclopentadienyl)] [η⁵-(2,7-dimethyl-3,6-di-tert-butyl fluorenyl)] zirconium dichloride;

di(p-tolyl) methylene [η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)] (η⁵-fluorenyl) zirconium dichloride, di(p-tolyl) methylene [η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)] [η⁵-(3,6-di-tert-butyl fluorenyl)]zirconium dichloride, di(p-tolyl) methylene [η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)] [η⁵-(2,7-di-tert-butyl fluorenyl)] zirconium dichloride, di(p-tolyl) methylene [η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)] (octamethyl octahydrodibenzofluorenyl) zirconium dichloride, di(p-tolyl) methylene [η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)](benzofluorenyl) zirconium dichloride, di(p-tolyl) methylene [η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)](dibenzofluorenyl) zirconium dichloride, di(p-tolyl) methylene [η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)](octahydrodibenzofluorenyl) zirconium dichloride, di(p-tolyl) methylene [η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)][η⁵-(2,7-diphenyl-3,6-di-tert-butyl fluorenyl)] zirconium dichloride, di(p-tolyl) methylene [η⁵-(3-tert-butyl-5-methyl cyclopentadienyl)][η⁵-(2,7-dimethyl-3,6-di-tert-butyl fluorenyl)] zirconium dichloride;

di(p-tolyl) methylene [η⁵-(3-tert-butyl cyclopentadienyl)] (η⁵-fluorenyl) zirconium dichloride, di(p-tolyl) methylene [η⁵-(3-tert-butyl cyclopentadienyl)] [η⁵-(3,6-di-tert-butyl fluorenyl)] zirconium dichloride, di(p-tolyl) methylene [η⁵-(3-tert-butyl cyclopentadienyl)] [η⁵-(2,7-di-tert-butyl fluorenyl)] zirconium dichloride, di(p-tolyl) methylene [η⁵-(3-tert-butyl cyclopentadienyl)](octamethyl octahydrodibenzofluorenyl) zirconium dichloride, di(p-tolyl) methylene [η⁵-(3-tert-butyl cyclopentadienyl)](benzofluorenyl) zirconium dichloride, di(p-tolyl) methylene [η⁵-(3-tert-butyl cyclopentadienyl)] (dibenzofluorenyl) zirconium dichloride, di(p-tolyl) methylene [η⁵-(3-tert-butyl cyclopentadienyl)] (octahydrodibenzofluorenyl) zirconium dichloride, di(p-tolyl) methylene [η⁵-(3-tert-butyl cyclopentadienyl)] [η⁵-(2,7-diphenyl-3,6-di-tert-butyl fluorenyl)] zirconium dichloride, di(p-tolyl) methylene [η⁵-(3-tert-butyl cyclopentadienyl)] [η⁵-(2,7-dimethyl-3,6-di-tert-butyl fluorenyl)] zirconium dichloride; and di(p-tolyl) methylene [η⁵-(3-n-butyl cyclopentadienyl)](η⁵-fluorenyl) zirconium dichloride, di(p-tolyl) methylene [η⁵-(3-n-butyl cyclopentadienyl)][η⁵-(3,6-di-tert-butyl fluorenyl)] zirconium dichloride, di(p-tolyl) methylene [η⁵-(3-n-butyl cyclopentadienyl)] [η⁵-(2,7-di-tert-butyl fluorenyl)] zirconium dichloride, di(p-tolyl) methylene [η⁵-(3-n-butyl cyclopentadienyl)] (octamethyl octahydrodibenzofluorenyl) zirconium dichloride, di(p-tolyl) methylene [η⁵-(3-n-butyl cyclopentadienyl)] (benzofluorenyl) zirconium dichloride, di(p-tolyl) methylene [η⁵-(3-n-butyl cyclopentadienyl)] (dibenzofluorenyl) zirconium dichloride, di(p-tolyl) methylene [η⁵-(3-n-butyl cyclopentadienyl)](octahydrodibenzofluorenyl) zirconium dichloride, di(p-tolyl) methylene [η⁵-(3-n-butyl cyclopentadienyl)] (2,7-diphenyl-3,6-di-tert-butyl fluorenyl) zirconium dichloride, di(p-tolyl) methylene [η⁵-(3-n-butyl cyclopentadienyl)] [η⁵-(2,7-dimethyl-3,6-di-tert-butyl fluorenyl)] zirconium dichloride.

Although compounds whose zirconium atoms were substituted with hafnium atoms, or compounds whose chloro ligands were substituted with methyl groups etc. are exemplified in these compounds, the bridged metallocene compound (a) is not limited to these exemplifications.

As the organoaluminum oxy-compound used in the catalyst system in the present invention, conventional aluminoxane can be used. For example, linear or ring type aluminoxane represented by the following Formulas 2 to 5 can be used. A small amount of organic aluminum compound may be contained in the organoaluminum oxy-compound.

In Formulae 2 to 4, R is independently a hydrocarbon group having 1 to 10 carbon atoms, Rx is independently a hydrocarbon group having 2 to 20 carbon atoms, m and n are independently an integer of 2 or more, preferably 3 or more, more preferably 10 to 70, and most preferably 10 to 50.

In Formula 5, R^(C) is a hydrocarbon group having 1 to 10 carbon atoms, and R^(d) is independently a hydrogen atom, halogen atom or hydrocarbon group having 1 to 10 carbon atoms.

In Formula 2 or Formula 3, R is a methyl group (Me) of the organoaluminum oxy-compound which is conventionally referred to as “methylaluminoxane”.

The methylaluminoxane is easily available and has high polymerization activity, and thus it is commonly used as an activator in the polyolefin polymerization. However, the methylaluminoxane is difficult to dissolve in a saturated hydrocarbon, and thus it has been used as a solution of aromatic hydrocarbon such as toluene or benzene, which is environmentally undesirable. Therefore, in recent years, a flexible body of methylaluminoxane represented by Formula 4 has been developed and used as an aluminoxane dissolved in the saturated hydrocarbon. The modified methylaluminoxane represented by Formula 4 is prepared by using a trimethyl aluminum and an alkyl aluminum other than the trimethyl aluminum as shown in U.S. Pat. Nos. 4,960,878 and 5,041,584, and for example, is prepared by using trimethyl aluminum and triisobutyl aluminum. The aluminoxane in which Rx is an isobutyl group is commercially available under the trade name of MMAO and TMAO, in the form of a saturated hydrocarbon solution. (See Tosoh Finechem Corporation, Tosoh Research & Technology Review, Vol 47, 55 (2003)).

As (ii) the compound which reacts with the bridged metallocene compound to form an ion pair (hereinafter, referred to as “ionic compound” as required) which is contained in the present catalyst system, a Lewis acid, ionic compounds, borane, borane compounds and carborane compounds can be used. These are described in patent literatures, Korean Patent No. 10-551147, JP H01-501950 A, JP H03-179005 A, JP H03-179006 A, JP H03-207703 A, JP H03-207704 A, U.S. Pat. No. 5,321,106 and so on. If needed, heteropoly compounds, and isopoly compound etc. can be used, and the ionic compound disclosed in JP 2004-51676 A can be used. The ionic compound may be used alone or by mixing two or more. In more detail, examples of the Lewis acid include the compound represented by BR₃ (R is fluoride, substituted or unsubstituted alkyl group having 1 to 20 carbon atoms (methyl group, etc.), substituted or unsubstituted aryl group having 6 to 20 carbon atoms (phenyl group, etc.), and also includes for example, trifluoro boron, triphenyl boron, tris(4-fluorophenyl) boron, tris(3,5-difluorophenyl) boron, tris(4-fluorophenyl) boron, tris(pentafluorophenyl) and boron tris(p-tolyl) boron. When the ionic compound is used, its use amount and sludge amount produced are relatively small in comparison with the organoaluminum oxy-compound, and thus it is economically advantageous. In the present invention, it is preferable that the compound represented by the following Formula 6 is used as the ionic compound.

In Formula 6, R^(e+) is H⁺, a carbenium cation, an oxonium cation, an ammonium cation, a phosphonium cation, a cycloheptyltrienyl cation, or a ferrocenium cation having a transition metal, and R^(f) to R^(i) each is independently an organic group, preferably a hydrocarbon group having 1 to 20 carbon atoms, and more preferably an aryl group, for example, a penta-fluorophenyl group. Examples of the carbenium cation include a tris(methylphenyl)carbenium cation and a tris(dimethylphenyl)carbenium cation, and examples of the ammonium cation include a dimethylanilinium cation.

Examples of compounds represented by the aforementioned Formula 6 preferably include N,N-dialkyl anilinium salts, and specifically include N,N-dimethylanilinium tetraphenylborate, N,N-dimethylanilinium tetrakis (pentafluorophenyl) borate, N,N-dimethylanilinium tetrakis (3,5-ditrifluoro methylphenyl) borate, N,N-diethyl anilinium tetraphenylborate, N,N-diethyl anilinium tetrakis (pentafluorophenyl) borate, N,N-diethyl anilinium tetrakis (3,5-ditrifluoro methylphenyl) borate, N,N-2,4,6-penta methylanilinium tetraphenylborate, and N,N-2,4,6-penta methylanilinium tetrakis (pentafluorophenyl) borate.

The catalyst system used in the present invention further includes (c) an organoaluminum compound when it is needed. The organoaluminum compound plays a role of activating the bridged metallocene compound, the organoaluminum oxy-compound, and the ionic compound, etc. As the organoaluminum compound, preferably an organoaluminum represented by the following Formula 7, and alkyl complex compounds of the Group 1 metal and aluminum represented by the following Formula 8 can be used.

R^(a) _(m)Al(OR^(b))_(n)H_(p)X_(q)  Formula 7

In Formula 7, R^(a) and R^(b) each is independently a hydrocarbon group having 1 to 15 carbon atoms, preferably 1 to 4 carbon atoms, and X is a halogen atom, m is an integer of 0<m≤3, n is an integer of 0≤n≤3, p is an integer of 0<p≤³, q is an integer of 0≤q<3, and m+n+p+q=3.

M²AlR^(a) ₄  Formula 8

In Formula 8, M² represents Li, Na or K, and R^(a) is a hydrocarbon group having 1 to 15 carbon atoms, and preferably 1 to 4 carbon atoms.

Examples of the organoaluminum compound represented by Formula 7 include trimethyl aluminum and triisobutyl aluminum etc., which are easily available. Examples of the alkyl complex compounds of Group 1 metal and aluminum represented by Formula 8 include LiAl(C₂H₅)₄, LiAl(C₇H₁₅)₄ etc. Compounds similar to the compounds represented by Formula 7 can be used. For example, like (C₂H₅)₂AlN(C₂H₅)Al (C₂H₅)₂, an organoaluminum compound to which at least 2 aluminum compounds are bonded through nitrogen atoms, can be used.

In the method for preparing the ethylene-α-olefin copolymer (B), the amount of (a) the bridged metallocene compound represented by Formula 1 is preferably 5 to 50% by weight with respect to total catalyst composition. Moreover, preferably the amount of (b) (i) the organoaluminum oxy-compound is 50 to 500 equivalent weight with respect to the molar number of the bridged metallocene compound to be used, the amount of (b) (ii) the compound which reacts with the bridged metallocene compound to form an ion pair is 1 to 5 equivalent weight with respect to the molar number of bridged metallocene compound to be used, and the amount of (c) the organoaluminum compound is 5 to 100 equivalent weight with respect to the molar number of the bridged metallocene compound to be used.

The catalyst system used in the present invention may have the following [1] to [4] for example.

[1] (a) the bridged metallocene compound represented by Formula 1, and (b) (i) the organoaluminum oxy-compound. [2] (a) the bridged metallocene compound represented by Formula 1, (b) (i) the organoaluminum oxy-compound and (c) the organoaluminum compound. [3] (a) the bridged metallocene compound represented by Formula 1, (b) (ii) the compound which reacts with the bridged metallocene compound to form an ion pair, and (c) the organoaluminum compound. [4] (a) bridged metallocene compound represented by Formula 1, and (b) (i) the organoaluminum oxy-compound and (ii) the compound which reacts with the bridged metallocene compound to form an ion pair.

(a) The bridged metallocene compound represented by Formula 1 (element (a)), (b) (i) the organoaluminum oxy-compound (element (b)), (ii) the compound which reacts with the bridged metallocene compound to form an ion pair and/or (c) the organoaluminum compound (element (c)) may be introduced in any order, to a starting raw material monomer (a mixture of ethylene and α-olefin having 3 to 20 carbon atoms). For example, elements (a), (b) and/or (c) are introduced alone or in any order, to a polymerization reactor with which raw material monomer is filled. Alternatively, if required, at least two elements among (a), (b) and/or (c) are mixed and then the mixed catalyst composition is introduced to the polymerization reactor with which raw material monomer is filled.

The ethylene-α-olefin copolymer (B) is prepared by a solution polymerization of ethylene and α-olefin having 3 to 20 carbon atoms under the catalyst system. As the α-olefin having 3 to 20 carbon atoms, one or more among linear α-olefins such as propylene, 1-butene, 1-penetene, 1-hexene etc., branched α-olefins such as isobutylene, 3-methyl-1-butene, 4-methyl-1-penetene etc. and mixtures thereof can be used. Preferably, one or more α-olefins having 3 to 6 carbon atoms can be used, and more preferably, propylene can be used. The solution polymerization can be carried out by using an inert solvent such as propane, butane or hexane etc. or an olefin monomer itself as a medium. In the copolymerization of ethylene and α-olefin of the present invention, the temperature for the copolymerization is usually 80 to 150° C. and preferably 90 to 120° C., and the pressure for the copolymerization is usually atmospheric pressure to 500 kgf/cm² and preferably atmospheric pressure to 50 kgf/cm², which can vary in accordance with reacting materials, reacting conditions, etc.

Batch-, semi-continuous- or continuous-type polymerization can be carried out, and continuous-type polymerization is preferably carried out.

The ethylene-α-olefin copolymer (B) is in liquid phase at room temperature, and has a structure where the α-olefin units are uniformly distributed in the copolymer chain. The ethylene-α-olefin copolymer (B) comprises e.g. 60 to 40 mol %, preferably 45 to 55 mol %, of ethylene units derived from ethylene, and further comprises e.g. 40 to 60 mol %, preferably 45 to 55 mol %, of α-olefin units having 3 to 20 carbon atoms which are derived from α-olefin having 3 to 20 carbon atoms.

The number average molecular weight (Mn) of the ethylene-α-olefin copolymer (B) is e.g. 500 to 10,000 and preferably 800 to 6,000, and the molecular weight distribution (Mw/Mn, Mw is weight average molecular weight) is e.g. 3 or less and preferably 2 or less. The number average molecular weight (Mn) and the molecular weight distribution (Mw/Mn) are measured by gel permeation chromatography (GPC).

The ethylene-α-olefin copolymer (B) has a kinematic viscosity at 100° C. of e.g. 30 to 5,000 and preferably 50 to 3,000 mm²/s, a pour point of e.g. 30 to −45° C. and preferably 20 to −35° C., and a Bromine Number of 0.1 g/100 g or less.

In the bridged metallocene compound represented by Formula 1, the polymerization activity is particularly high with respect to the copolymerization of ethylene with α-olefin. Utilizing this bridged metallocene compound selectively stops polymerization by hydrogen introduction at the molecular terminals, and thus there is little unsaturated bonding of the resulting ethylene-α-olefin copolymer (B). Moreover, since the ethylene-α-olefin copolymer (B) has a high random copolymerization, it has a controlled molecular weight distribution, and thus has excellent shear stability and viscosity properties. Therefore, it is considered that the lubricating oil composition for hydraulic oils of the present invention containing the ethylene-α-olefin copolymer (B) has remarkably excellent temperature viscosity properties, namely, has oil film retention properties at high temperatures and low-temperature viscosity properties, and further has excellent thermal and oxidation stability.

<Lubricating Oil Composition for Hydraulic Oils>

The lubricating oil composition for hydraulic oils according to the present invention contains the lubricant base oil (A) and the ethylene-α-olefin copolymer (B), and has the properties of the below (C1).

(C1) The lubricating oil composition for hydraulic oils has a kinematic viscosity at 40° C. of 10 to 300 mm²/s

The kinematic viscosity at 40° C. (kinematic viscosity measured in accordance with the method described in JIS K2283) is 10 to 300 mm²/s, preferably 20 to 250 mm²/s, more preferably 20 to 200 mm²/s, and further preferably 20 to 100 mm²/s. If the kinematic viscosity at 40° C. of the lubricating oil composition for hydraulic oils is excessively more than 300 mm²/s, the stirring torque during stirring of the lubricating oil composition is increased, and energy saving of hydraulic system using the lubricating oil composition is deteriorated. If it is excessively lower than 10 m²/s, an oil film of the lubricating oil composition cannot be maintained, and sufficient lubricity cannot be achieved.

The viscosity of products of industrial lubricating oils is generally defined by a kinematic viscosity at 40° C. The viscosity range is determined by JIS K2001 (in accordance with ISO 3448). An allowable range of ±10% with respect to each viscosity as a center is set. For example, a lubricating oil in which the kinematic viscosity at 40° C. is 68 mm²/s is called ISO VG68, and the allowable range of the kinematic viscosity at 40° C. is 61.2 to 74.8 mm²/s. A suitable range differs depending on the type of the hydraulic system, and use conditions. As a hydraulic oil, ISO VG32 to ISO VG220 are preferably used. As comparison of performance, comparison of lubricating oil compositions of equivalent viscosity grades is usually performed.

It is preferable that the lubricating oil composition for hydraulic oils according to the present invention further has properties of the below (C2).

(C2) The lubricating oil composition for hydraulic oils has a viscosity index of 120 or more

This viscosity index (viscosity index measured in accordance with the method described in JIS K2283) is preferably 120 or more, more preferably 130 or more, further preferably 140 or more, and particularly preferably 150 or more. With a viscosity index in this range, the lubricating oil composition has excellent temperature viscosity properties, and both energy saving and lubricity can be achieved over a wide range of temperature.

The pour point (pour point measured in accordance with the method described in ASTM D97) of the lubricating oil composition for hydraulic oils according to the present invention is preferably −20° C. or lower, more preferably −30° C. or lower, and further preferably −40° C. or lower. A low pour point indicates that the lubricating oil composition has excellent low-temperature properties.

The lubricating oil composition for hydraulic oils of the present invention contains the lubricant base oil (A) in an amount of 10 to 99% by mass, and the ethylene-α-olefin copolymer (B) in an amount of 90 to 1% by mass. The total amount of the lubricant base oil (A) and the ethylene-α-olefin copolymer (B) is 100% by mass. The lubricating oil composition for hydraulic oils of the present invention preferably contains the lubricant base oil (A) in an amount of 50 to 99% by mass, and the ethylene-α-olefin copolymer (B) in an amount of 50 to 1% by mass, more preferably the lubricant base oil (A) in an amount of 70 to 99% by mass, and the ethylene-α-olefin copolymer (B) in an amount of 30 to 1% by mass, and further preferably the lubricant base oil (A) in an amount of 80 to 99% by mass, and the ethylene-α-olefin copolymer (B) in an amount of 20 to 1% by mass.

A preferred aspect includes an aspect in which 30 to 100% by mass of the lubricant base oil is a mineral oil. When the ratio of the mineral oil occupying the lubricant base oil (A) is high, the solubility of an additive described below is excellent, the lubricant base oil has easy availability and excellent cost efficiency. The ratio of the mineral oil is more preferably 50 to 100% by mass, and further preferably 80 to 100% by mass. In mineral oils, a mineral oil of Group III in the API category is preferred since the mineral oil has excellent temperature viscosity properties and achieves both oil film retention at high temperatures and low torque under low temperatures.

Another preferred aspect includes an aspect in which 30 to 100% by mass of the lubricant base oil is a synthetic oil which is a poly-α-olefin and/or an ester oil. The ratio of the synthetic oil is more preferably 50 to 100% by mass, and further preferably 80 to 100% by mass. It is preferable that the ratio of the synthetic oil occupying the lubricant base oil (A) is high. This is because excellent heat resistance, temperature viscosity properties, and low-temperature properties are achieved.

Moreover, additives such as extreme pressure agents, detergent dispersants, viscosity index improving agents, antioxidants, corrosion preventing agents, anti-wear agents, friction modifying agents, pour point lowering agents, anti-rust agents and anti-foamers may be contained in the lubricating oil composition for hydraulic oils of the present invention.

Below are exemplifications of additives which can be utilized in the lubricating oil composition of the present invention, where these can be used alone, or used in combination of two or more.

The extreme pressure agent is the generic name for agents having a seizure preventing effect when metals are exposed to a high load condition, and although there are no particular limitations on the agent, sulfur-based extreme pressure agents such as sulfides, sulfoxides, sulfones, thiophosphinates, thiocarbonates, sulfurized oils and sulfurized olefins; phosphoric acids such as phosphate esters, phosphite esters, phosphate ester amine salts, and phosphite ester amines; and halogen-based compounds such as chlorinated hydrocarbons can be exemplified. Moreover, two or more types of these compounds may be used together.

Until extreme pressure lubricating conditions are attained, hydrocarbon or other organic components constituting lubricating oil composition may become carbonized before reaching extreme pressure lubricating conditions due to heating or shearing, and thus there is a possibility that a carbide film could be formed on a metal surface. Therefore, with the use of an extreme pressure agent alone, contact of a metal surface with the extreme pressure agent could be inhibited due to the carbide film, and thus a possibility that a sufficient effect of the extreme pressure agent cannot be expected.

Although the extreme pressure agent may be added alone, because a saturated hydrocarbon such as the copolymer constitutes a main component in the lubricating oil composition for hydraulic oils in the present invention, from the perspective of dispersibility, it is preferable to add the agent to the lubricant base oil such as mineral oil or synthetic hydrocarbon oil, together with the other additives to be used, in a dissolved state beforehand. Specifically, more preferable is a method of selecting the so-called additive package to be added to the lubricating oil composition, in which the various components such as the extreme pressure agent components are mixed in advance, and further dissolved in the lubricant base oil such as mineral oil or synthetic hydrocarbon oil.

Preferred examples of additive package include Anglamol-98A, Anglamol-6043, Angramol 6085U, and LUBIZOL 1047U (made by LUBRIZOL), HITEC 1532 (made by AFTON CHEMICAL), HITEC 307 (made by AFTON CHEMICAL), and HITEC 3339 made by AFTON CHEMICAL, and Additin RC 9410 (made by RHEIN CHEMIE).

The extreme pressure agent may be used as required in a range of 0 to 10% by mass, to 100% by mass of the lubricating oil composition.

Exemplifications of the anti-wear agent include inorganic or organic molybdenum compounds such as molybdenum disulfide, graphite, antimony sulfide, and polytetrafluoroethylene. The anti-wear agent may be used as required in a range of 0 to 3% by mass with respect to 100% by mass of the lubricating oil composition.

Exemplifications of the friction modifying agent include amine compounds, imide compound, fatty acid esters, fatty acid amides, and fatty acid metal salts having at least one alkyl group or alkenyl group having 6 to 30 carbon atoms, particularly linear alkyl groups or linear alkenyl groups having 6 to 30 carbon atoms, in a molecule.

Exemplifications of the amine compound include a linear- or branched-, preferably linear-, aliphatic monoamine, or a linear- or branched-, preferably linear-, aliphatic polyamine having 6 to 30 carbon atoms, or alkylene oxide adducts of these aliphatic amines. Examples of the imide compound include imide succinate with linear- or branched-alkyl group or alkenyl group having 6 to 30 carbon atoms and/or compounds thereof modified by a carboxylic acid, boric acid, phosphoric acid, sulfuric acid etc. Exemplifications of the fatty acid ester include esters of a linear- or branched-, preferably linear-, fatty acid having 7 to 31 carbon atoms with an aliphatic monohydric alcohol or aliphatic polyhydric alcohol. Exemplifications of the fatty acid amide include amides of a linear- or branched-, preferably linear-, fatty acid having 7 to 31 carbon atoms with an aliphatic monoamine or aliphatic polyamine. Examples of fatty acid metal salts include alkaline-earth metal salts (e.g. magnesium salts and calcium salts) and zinc salts of a linear- or branched-, preferably linear-, fatty acid having 7 to 31 carbon atoms.

The friction modifying agent may be used as required in a range of 0.01 to 5.0% by mass with respect to 100% by mass of the lubricating oil composition.

Exemplifications of detergent dispersants include metal sulfonates, metal phenates, metal phosphonates, and imide succinate. The detergent dispersant may be used as required in a range of 0 to 15% by mass with respect to 100% by mass of the lubricating oil composition.

In addition to ethylene-α-olefin copolymers (excluding the ethylene-α-olefin copolymer (B)), known viscosity index improving agents such as olefin copolymers whose molecular weights exceed 50,000, methacrylate-based copolymers, liquid polybutene, and poly-α-olefins having a kinematic viscosity at 100° C. of 15 mm²/s or more can be used together as the viscosity index improving agent. The viscosity index improving agent may be used as required in a range of 0 to 50% by mass with respect to 100% by mass of the lubricating oil composition.

Examples of the antioxidant include phenol-based or amine-based compounds such as 2,6-di-t-butyl-4-methylphenol. The antioxidant may be used as required in a range of 0 to 3% by mass with respect to 100% by mass of the lubricating oil composition.

Examples of the corrosion preventing agent include compounds such as benzotriazole, benzoimidazole, and thiadiazole. The corrosion preventing agent may be used as required in a range of 0 to 3% by mass with respect to 100% by mass of the lubricating oil composition.

Examples of the anti-rust agent include compounds such as amine compounds, carboxylic acid metal salts, polyhydric alcohol esters, phosphorus compounds, and sulfonates. The anti-rust agent may be used as required in a range of 0 to 3% by mass with respect to 100% by mass of the lubricating oil composition.

Exemplifications of the anti-foamer include silicone-based compounds such as dimethyl siloxane and silica gel dispersions, and alcohol- or ester-based compounds. The anti-foamer may be used as required in a range of 0 to 0.2% by mass with respect to 100% by mass of the lubricating oil composition.

A variety of known pour point lowering agents may be used as the pour point lowering agent. Specifically, high molecular compounds containing an organic acid ester group may be used, and in particular, vinyl polymers containing an organic acid ester group are suitably used. Examples of the vinyl polymer containing an organic acid ester group include (co)polymers of methacrylic acid alkyl, (co)polymers of acrylic acid alkyl, (co)polymers of fumaric acid alkyl, (co)polymers of maleic acid alkyl, and alkylated naphthalene.

Such pour point lowering agents have a melting point of −13° C. or lower, preferably −15° C., and furthermore preferably −17° C. or lower. The melting point of the pour point lowering agent was measured by means of differential scanning calorimetry (DSC). Specifically, a sample of about 5 mg was packed into an aluminum pan and temperature was raised to 200° C., where the temperature was maintained at 200° C. for 5 minutes. This was then cooled at 10° C./minute until reaching −40° C., where the temperature was maintained at −40° C. for 5 minutes. The temperature was then raised at 10° C./minute during which the melting point was obtained from the heat absorption curve.

The pour point lowering agent has a polystyrene conversion weight average molecular weight obtainable by gel permeation chromatography in the range of 20,000 to 400,000, preferably 30,000 to 300,000, and more preferably 40,000 to 200,000.

Thew pour point lowering agent may be used as required in a range of 0 to 2% by mass with respect to 100% by mass of the lubricating oil composition.

In addition to the aforementioned additives, anti-emulsifying agents, coloring agents, oiliness agents (oiliness improving agents) and the like may also be used as required.

<Use>

The lubricating oil composition of the present invention is suitably applicable to hydraulic oils of various industrial machinery and transportation machinery, and has remarkably excellent temperature viscosity properties, namely, oil film retention properties at high temperatures and low-temperature viscosity properties. Therefore, the lubricating oil composition can greatly contribute to energy saving of a hydraulic system. In particular, the lubricating oil composition of the present invention is remarkably useful as a hydraulic oil for machine tools, or a hydraulic oil for molding machines.

EXAMPLES

The present invention is further specifically explained based on the below Examples. However, the present invention is not limited to these Examples.

[Evaluation Method]

In the below Examples and Comparative Examples etc., the physical properties etc. of the ethylene-α-olefin copolymer and the hydraulic oil were measured by the below methods.

<Ethylene Content (Mol %)>

Using a Fourier transform infrared spectrometer FT/IR-610 or FT/IR-6100 (made by JASCO), the absorbance ratio of the absorption in the vicinity of 721 cm-1 based on the horizontal vibration of the long chain methylene group, and the absorption in the vicinity of 1155 cm-1 based on the skeletal vibration of propylene (D1155 cm-1/D721 cm-1) was calculated, and the ethylene content (% by weight) was obtained by the calibration curve created beforehand (created using the ASTM D3900 reference sample). Using the ethylene content (% by weight) thus obtained, the ethylene content (mol %) was obtained according to the following Formula.

${{Ethylene}\mspace{14mu}{content}\mspace{14mu}\left( {{mol}\mspace{20mu}\%} \right)} = \frac{\left\lbrack {{ethylene}\mspace{14mu}{content}\mspace{14mu}{\left( {\%\mspace{14mu}{by}\mspace{14mu}{weight}} \right)/28}} \right\rbrack}{\left\lbrack {{ethylene}\mspace{14mu}{content}\mspace{14mu}{\left( {\%\mspace{14mu}{by}\mspace{14mu}{weight}} \right)/28}} \right\rbrack + \left\lbrack {{propylene}\mspace{14mu}{content}\mspace{14mu}{\left( {\%\mspace{14mu}{by}\mspace{14mu}{weight}} \right)/42}} \right\rbrack}$

<B-Value>

Employing o-dichloro benzene/benzene-d₆ (4/1 [vol/vol %) as a measurement solvent, the ¹³C-NMR spectrum was measured under the measuring conditions (100 MHz, ECX 400P, made by JEOL Ltd) of temperature of 120° C., spectral width of 250 ppm, pulse repeating time of 5.5 seconds, and a pulse width of 4.7 μsec (45° pulse), or under the measuring conditions (125 MHz, AVANCE III cryo-500 made by Bruker Biospin Inc) of temperature of 120° C., spectral width of 250 ppm, pulse repeating time of 5.5 seconds, and a pulse width of 5.0 μsec (45° pulse), and the B-value was calculated based on the following Formula [1]. The peak attribution was performed by reference to the aforementioned known literature.

$\begin{matrix} {B = \frac{P_{OE}}{2{P_{O} \cdot P_{E}}}} & \lbrack 1\rbrack \end{matrix}$

In Formula [1], P_(E) indicates the molar fraction contained in the ethylene component, P_(O) indicates the molar fraction contained in the α-olefin component, and P_(OE) indicates the molar fraction of the ethylene-α-olefin sequences of all dyad sequences.

<Molecular Weight Distribution>

Employing the HLC-8320 GPC (gel permeation chromatography) device produced by Tosoh Corporation, the molecular weight distribution was measured as below. Four TSK gel Super Multipore HZ-M columns were used as separation columns, the column temperature was 40° C., tetrahydrofuran (made by Wako Pure Chemical Industries) was used as the mobile phase, with a development rate of 0.35 ml/minute, a sample concentration of 5.5 g/L, a sample injection amount of 20 microliters, and a differential refractometer was used as a detector. PStQuick MP-M; made by Tosoh Corporation) was used as the reference polystyrene. In accordance with general-purpose calibration procedures, weight average molecular weight (Mw) and number average molecular weight (Mn) were calculated in terms of polystyrene molecular weight, and the molecular weight distribution (Mw/Mn) was calculated from those values.

<Viscosity Properties>

The kinematic viscosity at 100° C., the kinematic viscosity at 40° C., and the viscosity index were measured and calculated by the method described in JIS K2283.

<Pour Point>

The pour point was measured by the method described in ASTM D97. Pour points lower than −50° C. were described as <−50 (° C.).

<−40° C. Viscosity>

Low-temperature viscosity properties were conducted in accordance with ASTM D2983, and the −40° C. viscosity was measured at −40° C. with a Brookfield viscometer.

<Thermal and Oxidation Stability>

Regarding thermal and oxidation stability, a test was conducted in accordance with the Oxidation Stability Test of Lubricating Oil for Internal Combustion Engines (ISOT) method described in JIS K2514, and the lacquer rating was evaluated 72 hours after the test time.

[Production of Ethylene-α-Olefin Copolymer (B)]

Ethylene-α-olefin copolymers (B) were prepared in accordance with the Polymerization Examples below.

Polymerization Example 1

760 ml of heptane and 120 g of propylene were charged into a stainless steel autoclave with a volume of 2 L sufficiently substituted with nitrogen, and the temperature in the system was raised to 150° C., and then 0.85 MPa of hydrogen and 0.19 MPa of ethylene were supplied to raise the total pressure to 3 MPaG. Then, 0.4 mmol of triisobutyl aluminum, 0.0002 mmol of diphenylmethylene [η⁵-(3-n-butyl cyclopentadienyl)] [η⁵-(2,7-di-tert-butyl fluorenyl)]zirconium dichloride, and 0.002 mmol of N,N-dimethylanilinium tetrakis (pentafluorophenyl) borate were injected with nitrogen, and polymerization was started by stirring with a rotation of 400 rpm. Ethylene was then continuously supplied to keep the total pressure at 3 MPaG, and polymerization took place at 150° C. for 5 minutes. Polymerization was stopped by adding a small amount of ethanol in the system, and the unreacted ethylene, propylene and hydrogen were purged. The resulting polymer solution was washed 3 times with 1000 ml of a 0.2 mol/L solution of hydrochloric acid, further washed 3 times with 1000 ml of distilled water, dried with magnesium sulfate, and the solvent was then distilled off under reduced pressure. The resulting polymer was dried at 80° C. under reduced pressure for 10 hours. The resulting polymer had an ethylene content of 49.5 mol %, an Mw of 5,100, an Mw/Mn of 1.7, a B-value of 1.2, and a 100° C. kinematic viscosity of 150 mm²/s.

Polymerization Example 2

710 mL of heptane and 145 g of propylene were charged into a stainless steel autoclave with a volume of 2 L sufficiently substituted with nitrogen, and the temperature in the system was raised to 150° C., and then 0.40 MPa of hydrogen and 0.27 MPa of ethylene were supplied to raise the total pressure to 3 MPaG. Then, 0.4 mmol of triisobutyl aluminum, 0.0001 mmol of diphenylmethylene [η⁵-(3-n-butyl cyclopentadienyl)][η⁵-(2,7-di-tert-butyl fluorenyl)]zirconium dichloride, and 0.001 mmol of N,N-dimethylanilinium tetrakis (pentafluorophenyl) borate were injected with nitrogen, and polymerization was started by stirring with a rotation of 400 rpm. Ethylene only was then continuously supplied to keep the total pressure at 3 MPaG, and polymerization took place at 150° C. for 5 minutes. Polymerization was stopped by adding a small amount of ethanol in the system, and the unreacted ethylene, propylene and hydrogen were purged. The resulting polymer solution was washed 3 times with 1000 ml of a 0.2 mol/L solution of hydrochloric acid, further washed 3 times with 1000 ml of distilled water, dried with magnesium sulfate, and the solvent was then distilled off under reduced pressure. The resulting polymer was dried overnight at 80° C. under reduced pressure to obtain 52.2 g of an ethylene-propylene copolymer. The resulting polymer had an ethylene content of 52.9 mol %, an Mw of 8,600, an Mw/Mn of 1.8, a B-value of 1.2, and a 100° C. kinematic viscosity of 600 mm²/s.

Polymerization Example 3

250 mL of heptane was charged into a glass polymerization vessel with a volume of 1 L sufficiently substituted with nitrogen, and the temperature in the system was raised to 50° C., and then 25 L/h of ethylene, 75 L/h of propylene, and 100 L/h of hydrogen were continuously supplied into the polymerization vessel, and stirred with a rotation of 600 rpm. Then, 0.2 mmol of triisobutyl aluminum was charged into the polymerization vessel, and 0.023 mmol of N,N-dimethylanilinium tetrakis (pentafluorophenyl) borate and 0.00230 mmol of diphenylmethylene [η⁵-(3-n-butyl cyclopentadienyl)] [η⁵-(2,7-di-tert-butyl fluorenyl)]zirconium dichloride, which were pre-mixed in toluene for 15 minutes or more, were charged into the polymerization vessel to start the polymerization. Ethylene, propylene and hydrogen were then continuously supplied, and polymerization took place at 50° C. for 15 minutes. Polymerization was stopped by adding a small amount of isobutyl alcohol in the system, and the unreacted monomers were purged. The resulting polymer solution was washed 3 times with 100 mL of a 0.2 mol/L solution of hydrochloric acid, further washed 3 times with 100 mL of distilled water, dried with magnesium sulfate, and the solvent was then distilled off under reduced pressure. The resulting polymer was dried overnight at 80° C. under reduced pressure to obtain 1.43 g of an ethylene-propylene copolymer. The resulting polymer had an ethylene content of 52.4 mol %, an Mw of 13,600, an Mw/Mn of 1.9, a B-value of 1.2, and a 100° C. kinematic viscosity of 2,000 mm²/s.

Polymerization Example 4

760 ml of heptane and 120 g of propylene were charged into a stainless steel autoclave with a volume of 2 L sufficiently substituted with nitrogen, and the temperature in the system was raised to 150° C., and then 0.85 MPa of hydrogen and 0.19 MPa of ethylene were supplied to raise the total pressure to 3 MPaG. Then, 0.4 mmol of triisobutyl aluminum, 0.0002 mmol of dimethylsilyl bis(indenyl) zirconium dichloride, and 0.059 mmol of MMAO were injected with nitrogen, and polymerization was started by stirring with a rotation of 400 rpm. Ethylene was then continuously supplied to keep the total pressure at 3 MPaG, and polymerization took place at 150° C. for 5 minutes. Polymerization was stopped by adding a small amount of ethanol in the system, and the unreacted ethylene, propylene and hydrogen were purged. The resulting polymer solution was washed 3 times with 1000 ml of a 0.2 mol/L solution of hydrochloric acid, further washed 3 times with 1000 ml of distilled water, dried with magnesium sulfate, and the solvent was then distilled off under reduced pressure. The resulting polymer was dried at 80° C. under reduced pressure for 10 hours. The the resulting polymer had an ethylene content of 48.5 mol %, an Mw of 5,000, an Mw/Mn of 1.8, a B-value of 1.2, and a 100° C. kinematic viscosity of 150 mm²/s.

Polymerization Example 5

710 mL of heptane and 145 g of propylene were charged into a stainless steel autoclave with a volume of 2 L sufficiently substituted with nitrogen, and the temperature in the system was raised to 150° C., and then 0.40 MPa of hydrogen and 0.27 MPa of ethylene were supplied to raise the total pressure to 3 MPaG. Then, 0.4 mmol of triisobutyl aluminum, 0.0001 mmol of dimethylsilyl bis(indenyl) zirconium dichloride, and 0.029 mmol of MMAO were injected with nitrogen, and polymerization was started by stirring with a rotation of 400 rpm. Ethylene only was then continuously supplied to keep the total pressure at 3 MPaG, and polymerization took place at 150° C. for 5 minutes. Polymerization was stopped by adding a small amount of ethanol in the system, and the unreacted ethylene, propylene and hydrogen were purged. The resulting polymer solution was washed 3 times with 1000 ml of a 0.2 mol/L solution of hydrochloric acid, further washed 3 times with 1000 ml of distilled water, dried with magnesium sulfate, and the solvent was then distilled off under reduced pressure. The resulting polymer was dried overnight at 80° C. under reduced pressure to obtain 52.2 g of an ethylene-propylene copolymer. The resulting polymer had an ethylene content of 53.3 mol %, an Mw of 8,500, an Mw/Mn of 1.9, a B-value of 1.2, and a 100° C. kinematic viscosity of 600 mm²/s.

Polymerization Example 6

250 mL of heptane was charged into a glass polymerization vessel with a volume of 1 L sufficiently substituted with nitrogen, and the temperature in the system was raised to 50° C., and then 25 L/h of ethylene, 75 L/h of propylene, and 100 L/h of hydrogen were continuously supplied into the polymerization vessel, and stirred with a rotation of 600 rpm. Then, 0.2 mmol of triisobutyl aluminum was charged into a polymerization vessel, and 0.688 mmol of MMAO and 0.00230 mmol of dimethylsilyl bis(indenyl) zirconium dichloride, which were pre-mixed in toluene for 15 minutes or more, were charged into a polymerization vessel to start the polymerization. Ethylene, propylene and hydrogen were then continuously supplied, and polymerization took place at 50° C. for 15 minutes. Polymerization was stopped by adding a small amount of isobutyl alcohol in the system, and the unreacted monomers were purged. The resulting polymer solution was washed 3 times with 100 mL of a 0.2 mol/L solution of hydrochloric acid, further washed 3 times with 100 mL of distilled water, dried with magnesium sulfate, and the solvent was then distilled off under reduced pressure. The resulting polymer was dried overnight at 80° C. under reduced pressure to obtain 1.43 g of an ethylene-propylene copolymer. The resulting polymer had an ethylene content of 52.1 mol %, an Mw of 13,800, an Mw/Mn of 2.0, a B-value of 1.2, and a 100° C. kinematic viscosity of 2,000 mm²/s.

The copolymer obtained by Polymerization Example 1, the copolymer obtained by Polymerization Example 2, the copolymer obtained by Polymerization Example 3, the copolymer obtained by Polymerization Example 4, the copolymer obtained by Polymerization Example 5, and the copolymer obtained by Polymerization Example 6 are respectively described below as Polymer 1, Polymer 2, Polymer 3, Polymer 4, Polymer 5, and Polymer 6.

Preparation of Lubricating Oil Composition for Hydraulic Oils

The components used other than the ethylene-α-olefin copolymer in the preparation of the below lubricating oil compositions are as follows.

Lubricant base oil; as a mineral oil, the following lubricant base oils were used.

Mineral oil-A: API (American Petroleum Institute) Group III mineral oil with a kinematic viscosity at 100° C. of 6.5 mm²/s, a viscosity index of 131, and a pour point of −12.5° C. (Yubase-6 made by SK Lubricants)

Mineral oil-B: API (American Petroleum Institute) Group I mineral oil with a kinematic viscosity at 100° C. of 6.8 mm²/s, a viscosity index of 108, and a pour point of −12.5° C. (Super oil N-32 made by JX Nippon Oil & Energy Corporation)

As a synthetic oil, the following lubricant base oils were used.

Synthetic oil-A: synthetic oil poly-α-olefin with a kinematic viscosity at 100° C. of 4.0 mm²/s, a viscosity index of 123, and a pour point of −50° C. or lower (NEXBASE2004 made by Neste)

Synthetic oil-B: synthetic oil poly-α-olefin with a kinematic viscosity at 100° C. of 5.8 mm²/s, a viscosity index of 138, and a pour point of −50° C. or lower (NEXBASE2006 made by Neste)

Synthetic oil-C: synthetic oil poly-α-olefin with a kinematic viscosity at 100° C. of 8.0 mm²/s, a viscosity index of 142, and a pour point of −50° C. (SpectraSyn (registered trademark) 8 made by ExxonMobil Chemical)

Synthetic oil-D: ester-based synthetic oil, trimethylolpropane caprylate (TMTC) with a kinematic viscosity at 100° C. of 4.5 mm²/s, a viscosity index of 142, and a pour point of −50° C. or lower, SYNATIVE (registered trademark) ES TMTC made by Cognis

In addition to the lubricant base oils and the ethylene-α-olefin copolymers, the following additives were used.

Pour point lowering agent (PPD)-A; IRGAFLOW 720P made by BASF

Additive package-A; HITEC-3339 made by Afton Chemical

Additive package-B; LUBRIZOL 1047UI made by LUBRIZOL

Antioxidant; phenolic antioxidant (Irganox L135 made by BASF)

<Lubricating Oil Composition for Hydraulic Oils> Example 1

As the lubricant base oil (A), Synthetic oil-A was used, and as the ethylene-α-olefin copolymer (B), the copolymer (Polymer 2) obtained in Polymerization Example 2 was used. These were mixed together with an antioxidant, and adjusted to 100% by mass, thereby preparing a lubricating oil composition for hydraulic oils. The addition amounts of the respective components are as shown in Table 2. Physical properties of the lubricating oil composition are shown in Table 2.

Examples 2 to 16 and Comparative Examples 1 to 7

Except for changing the types of components and addition amounts to those as described in Table 2, the lubricating oil compositions for hydraulic oils were prepared in the same way as in Example 1. Physical properties, and the like of the obtained lubricating oil compositions are as shown in Table 2.

TABLE 2 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Polymer 1 % by mass Polymer 2 % by mass 11.0 10.0 7.0 Polymer 3 % by mass 8.0 8.0 6.0 Polymer 4 % by mass Polymer 5 % by mass Polymer 6 % by mass Mineral oil - A % by mass 92.3 93.3 Mineral oil - B % by mass Synthetic oil - A % by mass 88.8 91.8 Synthetic oil - B % by mass 88.8 91.8 Synthetic oil - C % by mass Synthetic oil - D % by mass Antioxidant % by mass 0.2 0.2 0.2 0.2 0.2 0.2 Additive % by mass package-A Additive % by mass package-B Pour point % by mass 0.5 0.5 lowering agent-A Kinematic mm²/s 46 47 68 68 67 70 viscosity at 40° C. Viscosity index — 170 175 158 158 148 153 Pour point ° C. <−50 <−50 <−50 <−50 −40° C. viscosity mPa · s 9,500 9,200 22,000 20,000 ISOT Lacquer Adhered Adhered Adhered Adhered Adhered Adhered rating substance substance substance substance substance substance (thin) (thin) (thin) (thin) (medium) (medium) Ex. 7 Ex. 8 Ex. 9 Ex. 10 Ex. 11 Ex. 12 Polymer 1 % by mass 39.0 Polymer 2 % by mass 15.0 21.0 24.0 Polymer 3 % by mass 11.0 16.0 Polymer 4 % by mass Polymer 5 % by mass Polymer 6 % by mass Mineral oil - A % by mass Mineral oil - B % by mass Synthetic oil - A % by mass Synthetic oil - B % by mass 84.8 88.8 78.8 83.8 Synthetic oil - C % by mass 49.8 64.8 Synthetic oil - D % by mass 10.0 10.0 Antioxidant % by mass 0.2 0.2 0.2 0.2 Additive % by mass 1.2 1.2 package-A Additive % by mass package-B Pour point % by mass lowering agent-A Kinematic mm²/s 98 100 148 158 230 230 viscosity at 40° C. Viscosity index — 161 163 167 159 161 168 Pour point ° C. −50 <−50 −43 −45 −40° C. viscosity mPa · s 44,000 38,000 75,000 76,000 ISOT Lacquer Adhered Adhered Adhered Adhered Adhered Adhered rating substance substance substance substance substance substance (medium) (medium) (medium) (medium) (medium) (medium) Comp. Comp. Ex. 13 Ex. 14 Ex. 15 Ex. 16 ex. 1 ex. 2 Polymer 1 % by mass 39.0 Polymer 2 % by mass 25.0 Polymer 3 % by mass 16.0 18.0 Polymer 4 % by mass Polymer 5 % by mass 11.0 Polymer 6 % by mass 8.0 Mineral oil - A % by mass Mineral oil - B % by mass 59.5 73.5 80.5 Synthetic oil - A % by mass 88.8 91.8 Synthetic oil - B % by mass Synthetic oil - C % by mass 72.8 Synthetic oil - D % by mass 10.0 Antioxidant % by mass 0.2 0.2 Additive % by mass 1.2 package-A Additive % by mass 1.0 1.0 1.0 package-B Pour point % by mass 0.5 0.5 0.5 lowering agent-A Kinematic mm²/s 228 223 222 216 46 47 viscosity at 40° C. Viscosity index — 167 150 160 164 170 175 Pour point ° C. <−50 <−50 −40° C. viscosity mPa · s 9,300 9,600 ISOT Lacquer Adhered Adhered Adhered Adhered Adhered Adhered rating substance substance substance substance substance substance (thin) (thin) (thin) (thin) (thick) (thick) Comp. Comp. Comp. Comp. Comp. ex. 3 ex. 4 ex. 5 ex. 6 ex. 7 Polymer 1 % by mass Polymer 2 % by mass Polymer 3 % by mass Polymer 4 % by mass 39.0 Polymer 5 % by mass 7.0 25.0 Polymer 6 % by mass 6.0 18.0 Mineral oil - A % by mass 92.3 93.3 Mineral oil - B % by mass 59.5 73.5 80.5 Synthetic oil - A % by mass Synthetic oil - B % by mass Synthetic oil - C % by mass Synthetic oil - D % by mass Antioxidant % by mass 0.2. 0.2 Additive % by mass package-A Additive % by mass 1.0 1.0 1.0 package-B Pour point % by mass 0.5 0.5 0.5 0.5 0.5 lowering agent-A Kinematic mm²/s 67 70 225 220 221 viscosity at 40° C. Viscosity index — 148 153 151 159 166 Pour point ° C. −40° C. viscosity mPa · s ISOT Lacquer Adhered Adhered Adhered Adhered Adhered rating substance substance substance substance substance (thick) (thick) (thick) (thick) (thick) 

1. A lubricating oil composition for hydraulic oils, comprising 10 to 99% by mass of a lubricant base oil (A) having the properties of the below (A1) to (A3), 90 to 1% by mass of a liquid random copolymer (B) of ethylene and α-olefin, the liquid random copolymer (B) being prepared by the below method (α), wherein the total amount of the lubricant base oil (A) and the copolymer (B) is 100% by mass, the lubricating oil composition having the properties of the below (C1). (A1) The lubricant base oil has a kinematic viscosity at 100° C. of 1 to 14 mm²/s. (A2) The lubricant base oil has a viscosity index of 100 or more. (A3) The lubricant base oil has a pour point of 0° C. or lower. (C1) The lubricating oil composition for hydraulic oils has a kinematic viscosity at 40° C. of 10 to 300 mm²/s. (Method (α)) A method (α) for preparing a liquid random copolymer of ethylene and α-olefin, comprising a step of carrying out solution polymerization of ethylene and α-olefin having 3 to 20 carbon atoms, under a catalyst system comprising (a) a bridged metallocene compound represented by the following Formula 1, and (b) at least one compound selected from a group consisting of (i) an organoaluminum oxy-compound, and (ii) a compound which reacts with the bridged metallocene compound to form an ion pair.

[In Formula 1, R¹, R², R³, R⁴, R⁵, R⁸, R⁹ and R¹² are respectively and independently hydrogen atom, hydrocarbon group or silicon-containing hydrocarbon group, and adjoining groups are optionally connected to each other to form a ring structure, R⁶ and R¹¹, being the same, are hydrogen atom, hydrocarbon group or silicon-containing hydrocarbon group, R⁷ and R¹⁰, being the same, are hydrogen atom, hydrocarbon group or silicon-containing hydrocarbon group, R⁶ and R⁷ are optionally connected to hydrocarbon having 2 to 3 carbon atoms to form a ring structure, R¹¹ and R¹⁰ are optionally connected to hydrocarbon having 2 to 3 carbon atoms to form a ring structure, R⁶, R⁷, R¹⁰ and R¹¹ are not hydrogen atom at the same time; Y is a carbon atom or silicon atom; R¹³ and R¹⁴ are independently aryl group; M is Ti, Zr or Hf; Q is independently halogen, hydrocarbon group, an anionic ligand or a neutral ligand which can be coordinated to a lone pair of electrons; and j is an integer of 1 to 4.]
 2. The lubricating oil composition for hydraulic oils according to claim 1, wherein in the metallocene compound represented by the above Formula 1, at least one among substituents (R¹, R², R³ and R⁴) bonded to a cyclopentadienyl group is a hydrocarbon group having 4 or more carbon atoms.
 3. The lubricating oil composition for hydraulic oils according to claim 1, wherein R⁶ and R¹¹, being the same, are hydrocarbon groups having 1 to 20 carbon atoms.
 4. The lubricating oil composition for hydraulic oils according to claim 1, wherein in the metallocene compound represented by the above Formula 1, substituent (R² or R³) bonded to the 3-position of the cyclopentadienyl group is a hydrocarbon group.
 5. The lubricating oil composition for hydraulic oils according to claim 4, wherein in the metallocene compound represented by the above Formula 1, the hydrocarbon group (R² or R³) bonded to the 3-position of the cyclopentadienyl group is an n-butyl group.
 6. The lubricating oil composition for hydraulic oils according to claim 1, wherein in the metallocene compound represented by the above Formula 1, the hydrocarbon group (R⁶ and R¹¹) bonded to the 2-position and 7-position of the fluorenyl group are all tert-butyl groups.
 7. The lubricating oil composition for hydraulic oils according to claim 1, wherein the compound which reacts with the bridged metallocene compound to form an ion pair is a compound represented by the following Formula
 6.

[In Formula 6, R^(e+) is H⁺, a carbenium cation, an oxonium cation, an ammonium cation, a phosphonium cation, a cycloheptyltrienyl cation, or a ferrocenium cation having a transition metal, and R^(f) to R^(i) each is independently a hydrocarbon group having 1 to 20 carbon atoms.]
 8. The lubricating oil composition for hydraulic oils according to claim 7, wherein the ammonium cation is a dimethylanilinium cation.
 9. The lubricating oil composition for hydraulic oils according to claim 7, wherein the catalyst system further comprises an organoaluminum compound selected from a group consisting of trimethyl aluminum and triisobutyl aluminum.
 10. The lubricating oil composition for hydraulic oils according to claim 1, wherein a content of the liquid random copolymer (B) is 1 to 20% by mass.
 11. A lubricating oil composition for hydraulic oils, comprising 10 to 99% by mass of a lubricant base oil (A) having the properties of the below (A1) to (A3), 90 to 1% by mass of a liquid random copolymer of ethylene and α-olefin having the properties of the below (B1) to (B5), wherein the total amount of the lubricant base oil (A) and the copolymer is 100% by mass, the lubricating oil composition having the properties of the below (C1). (A1) The lubricant base oil has a kinematic viscosity at 100° C. of 1 to 14 mm²/s. (A2) The lubricant base oil has a viscosity index of 100 or more. (A3) The lubricant base oil has a pour point of 0° C. or lower. (B1) The liquid random copolymer comprises 40 to 60 mol % of ethylene units and 60 to 40 mol % of α-olefin units having 3 to 20 carbon atoms. (B2) The liquid random copolymer has a number average molecular weight (Mn) of 500 to 10,000 and a molecular weight distribution (Mw/Mn, Mw is the weight average molecular weight) of 3 or less, as measured by gel permeation chromatography (GPC). (B3) The liquid random copolymer has a kinematic viscosity at 100° C. of 30 to 5,000 mm²/s. (B4) The liquid random copolymer has a pour point of 30 to −45° C. (B5) The liquid random copolymer has a Bromine Number of 0.1 g/100 g or less. (C1) The lubricating oil composition for hydraulic oils has a kinematic viscosity at 40° C. of 10 to 300 mm²/s.
 12. The lubricating oil composition for hydraulic oils according to claim 1, wherein the lubricant base oil (A) further satisfies the below (A4) to (A6). (A4) The lubricant base oil has a kinematic viscosity at 100° C. of 1 to 10 mm²/s. (A5) The lubricant base oil has a viscosity index of 110 or more. (A6) The lubricant base oil has a pour point of −10° C. or lower.
 13. The lubricating oil composition for hydraulic oils according to claim 1, wherein 30 to 100% by mass of the lubricant base oil (A) is a mineral oil.
 14. The lubricating oil composition for hydraulic oils according to claim 1, wherein 30 to 100% by mass of the lubricant base oil (A) is a synthetic oil, and the synthetic oil is poly-α-olefin (PAO) and/or an ester oil.
 15. The lubricating oil composition for hydraulic oils according to claim 1, wherein the kinematic viscosity at 40° C. is 20 to 100 mm²/s.
 16. A hydraulic oil for machine tools or molding machines comprising the lubricating oil composition for hydraulic oils according to claim
 1. 17. A method for producing a lubricating oil composition for hydraulic oils, comprising the steps of: preparing a liquid random copolymer (B) of ethylene and α-olefin by the following method (α); preparing a lubricating oil composition for hydraulic oils by a lubricant base oil (A) having the properties of the below (A1) to (A3) in an amount of 10 to 99% by mass in the lubricating oil composition with the liquid random copolymer (B) in an amount of 1 to 90% by mass in the lubricating oil composition, wherein the total amount of the lubricant base oil (A) and the copolymer (B) is 100% by mass, the composition having the properties of the below (C1). (A1) The lubricant base oil has a kinematic viscosity at 100° C. of 1 to 14 mm²/s. (A2) The lubricant base oil has a viscosity index of 100 or more. (A3) The lubricant base oil has a pour point of 0° C. or lower. (C1) The lubricating oil composition for hydraulic oils has a kinematic viscosity at 40° C. of 10 to 300 mm²/s. (Method (α)) A method (α) for preparing a liquid random copolymer of ethylene and α-olefin, comprising a step of carrying out solution polymerization of ethylene and α-olefin having 3 to 20 carbon atoms, under a catalyst system comprising (a) a bridged metallocene compound represented by the following Formula 1, and (b) at least one compound selected from a group consisting of (i) an organoaluminum oxy-compound, and (ii) a compound which reacts with the bridged metallocene compound to form an ion pair.

[In Formula 1, R¹, R², R³, R⁴, R⁵, R⁸, R⁹ and R¹² are respectively and independently hydrogen atom, hydrocarbon group or silicon-containing hydrocarbon group, and adjoining groups are optionally connected to each other to form a ring structure, R⁶ and R¹¹, being the same, are hydrogen atom, hydrocarbon group or silicon-containing hydrocarbon group, R⁷ and R¹⁰, being the same, are hydrogen atom, hydrocarbon group or silicon-containing hydrocarbon group, R⁶ and R⁷ are optionally connected to hydrocarbon having 2 to 3 carbon atoms to form a ring structure, R¹¹ and R¹⁰ are optionally connected to hydrocarbon having 2 to 3 carbon atoms to form a ring structure, R⁶, R⁷, R¹⁰ and R¹¹ are not hydrogen atom at the same time; Y is a carbon atom or silicon atom; R¹³ and R¹⁴ are independently aryl group; M is Ti, Zr or Hf; Q is independently halogen, hydrocarbon group, an anionic ligand or a neutral ligand which can be coordinated to a lone pair of electrons; and j is an integer of 1 to 4.] 